Disk drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disk medium, the actual information being stored in the form of magnetic transitions within the medium. The disks themselves are rotatably mounted on a spindle. The information is accessed by using read/write heads generally located on a pivoting arm that moves radially over the surface of the disk. The read/write heads or transducers must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
During operation, the disks are rotated at very high speeds within an enclosed housing using an electric motor that is generally located inside a hub that supports the disks. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle using two ball or hydrodynamic bearings mounted to a motor shaft disposed in the center of the hub.
In a hydrodynamic bearing, a bearing has two spaced-apart surfaces, mounted respectively on two relatively rotating members (typically a shaft and a surrounding sleeve), with a lubricating fluid such as air, gas or oil providing a bearing between them. In one design, a bearing surface is positioned proximate each end of the shaft and is spaced apart from another bearing surface mounted on the rotor hub. A volume containing the lubricating fluid (a gap) is therefore formed between the bearing surfaces. The gap between the bearing surfaces must be repeatable from disk drive to disk drive in the manufacturing process.
The conventional technique for setting a gap in a bearing comprises mounting a lower bearing component onto a shaft after the shaft has been secured to a support. A rotor hub having a central journal sleeve and a bearing surface affixed thereon is then mounted onto the shaft in a spaced apart relation to the lower bearing component, and an amount of hydrodynamic fluid is added into the rotor hub's journal sleeve. An upper bearing is then pressed onto the rotor shaft in a spaced apart relation to the rotor hub to complete the assembly.
One problem with this conventional technique, however, is that it compresses the shaft between the bearing surfaces, enlarging the shaft diameter and causing additional stiction between the shaft and the bearing surfaces. The problem is further complicated when the shaft is compressed to an enlarged diameter that is greater than the actual gap that must be set; consequently the hydrodynamic bearing cannot be properly formed.
Therefore, there is a need in the art for a method that can accurately and repeatably set these gaps while allowing for rapid motor assembly.